feat(select): poll/select and fd_set

include/poll.h

@@ -0,0 +1,99 @@
+#ifndef VLIBC_POLL_H
+#define VLIBC_POLL_H
+
+/*
+ * vlibc — <poll.h>.
+ *
+ * Poll multiple file descriptors for readiness. Every declaration here is a
+ * thin pass-through to the kernel: poll() blocks per its millisecond
+ * timeout, ppoll() takes a struct timespec and an optional signal mask
+ * directly, and both return the count of ready descriptors (0 on timeout,
+ * -1 with errno set on error).
+ *
+ *   Level 1 (onlyposix): poll, nfds_t, struct pollfd, the POLL* event bits.
+ *   Level 2 (muslmimic): ppoll (Linux-specific; POSIX has only poll).
+ *
+ * struct pollfd and the POLL* values mirror the kernel ABI (x86_64
+ * asm-generic/poll.h) exactly: the wrappers pass them to SYS_ppoll
+ * unmodified. POLLERR, POLLHUP and POLLNVAL are report-only — they can
+ * appear in revents even when not requested in events.
+ *
+ * The signal mask type ppoll takes is declared under the shared guard
+ * below; <signal.h> is its canonical POSIX home and will own the full sig*
+ * API.
+ */
+
+#include <vlibc/features.h>
+
+#include <sys/types.h>
+
+#include <time.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Requestable event bits (poll()'s events field). */
+#define POLLIN 0x001  /* readable */
+#define POLLPRI 0x002 /* urgent readable (out-of-band) */
+#define POLLOUT 0x004 /* writable */
+
+/* Report-only event bits (poll()'s revents field). */
+#define POLLERR 0x008  /* error condition */
+#define POLLHUP 0x010  /* hung up */
+#define POLLNVAL 0x020 /* invalid fd */
+
+/* The number of struct pollfd entries poll()/ppoll() watch. */
+typedef unsigned long nfds_t;
+
+/*
+ * One descriptor watched by poll()/ppoll(). fd is the descriptor (negative
+ * to ignore), events the requested bits (POLLIN/POLLOUT), revents the bits
+ * the kernel reports (the requested bits plus any POLLERR/POLLHUP/POLLNVAL).
+ */
+struct pollfd
+{
+    int fd;
+    short events;
+    short revents;
+};
+
+/*
+ * Wait for readiness on the first nfds entries of fds, blocking up to
+ * timeout milliseconds (timeout < 0 blocks indefinitely, 0 never blocks).
+ * Return the number of entries with a nonzero revents, 0 on timeout, or -1
+ * with errno set on error.
+ */
+int
+poll(struct pollfd *fds, nfds_t nfds, int timeout);
+
+#if VLIBC_LEVEL_GE(2)
+/* Level 2 (muslmimic): Linux-specific. */
+
+#ifndef VLIBC_SIGSET_T_DEFINED
+#define VLIBC_SIGSET_T_DEFINED
+/*
+ * Signal mask type: a single 64-bit word — the x86_64 Linux sigset_t (see
+ * setjmp.h). <signal.h> is the canonical POSIX home for sigset_t and builds
+ * the sig* API on this same layout; the typedef is repeated in
+ * <sys/select.h> under this guard so the two headers stay consistent.
+ */
+typedef unsigned long sigset_t;
+#endif
+
+/*
+ * Like poll(), but the timeout is a struct timespec and, when sigmask is
+ * not NULL, the given signal mask is atomically installed for the duration
+ * of the wait (the previous mask is restored before returning).
+ * Linux-specific.
+ */
+int
+ppoll(struct pollfd *fds, nfds_t nfds, const struct timespec *timeout, const sigset_t *sigmask);
+
+#endif /* VLIBC_LEVEL_GE(2) */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* VLIBC_POLL_H */